High reactance transformer



March 18, 1958 c. E. STRECKER HIGH REACTANCE TRANSFORMER MJJM'J M3 24 ttor'ney- Filed July 19, 1955 [ml/$722302": Char/es iitrecke United States Patent 2,827,614 7 HIGH REACTANCE TRANSFORMER Charles E. Strecker, Danville, Ill., assignor to General Electric Company, a corporation of New York Application July 19, 1955, Serial No. 522,974

6 Claims. (Cl. 336-165) This invention relates to inductive devices, and more particularly to high reactance transformers.

High reactance transformers are alternating current inductive devices which either step up or step down a voltage and also provide a substantial current limiting impedance. Such transformers are commonly used for operating arc discharge devices, such as fluorescent lamps, since they provide the requisite high voltage for breaking down or starting the lamp, and subsequently limit the lamp current to a safe value. When thus used, high reactance transformers are generally referred to as ballasts. In such transformers, the core provides a path for the mutual flux which links the coils of the transformer and also provides a separate magnetic path for the leakage flux, that is, the flux produced by the load current flowing in the secondary. winding. The path for leakage flux may be a shunt formed of magnetic material, frequently integral with the remainder of the core, or may be provided by suitable arrangement of the coils on the core.

In the past, the cores of high reactance transformers have generally been formed from stacks of relatively thin laminations of magnetic material where each lamination is punched from a thin sheet of magnetic material. This has resulted in substantial waste of material with a consequent increase in the overall cost of the device. In order to reduce the amount of magnetic material required for high reactance transformers, it becomes necessary to resort to a wound core where the core, instead of being built up of a stackof punched laminations, is Wound from a narrow strip of relatively thin magnetic material. An improved type of wound core which effects a substantial saving in material is, for instance, set forth in application Serial No. 467,304, filed November 8, 1954, by Wayne Lee Roy Henderson and assigned to the assignee of the present application. That application sets forth a structure in which the wound core does not need to be cut to assemble the coils thereon and which incorporates the necessary magnetic shunts and series air gaps of a high reactance transformer. While the structure set forth in that application successfully reduces to a considerable extent the amount of material required in the manufacture of a high reactance transformer, it remains highly desirable to reduce still further the amount of material needed.

it is, therefore, an object of this invention to provide an improved high reactance transformer which incorporates the desirable feature of a minimum usage of magnetic material to carry a given amount of flux.

Further objects and advantages of this invention will become apparent and the invention will be better understood by reference to the following description and the accompanying drawing, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification;

In its broadest aspect, this invention provides a high reactance transformer which includes an elongated core 2,327,614 Patented Mar. 18, 1958 member formed of magnetic material, with at least two spaced apart coils being positioned on the core member and respectively spaced from the end portions thereof. A first yoke core member is formed of a wound strip of magnetic materialso as to embrace one of the coils and abut a side of one of the elongated core member end portions. A second yoke core member is similarly formed of a wound strip of magnetic material so as to embrace another of the coils and abut a side of the other of the elongated core member end portions. At least one of the yoke core members is arranged adjacent the elongated core member intermediate the coils so as to form a magnetic shunt for the transformer. A third yoke core member is formed from a wound strip of magnetic material so as to embrace both of the coils and the first and second yoke core members. This third member is further arranged to abut a side of each of the elongated core member end portions, and is wound in a plane substantially perpendicular to the planes in which the first and second yoke core members are wound.

in the drawing, Figure l is a view in perspective, partly cut away, of the improved high reactance transformer of this invention;

Figure 2 is a view in perspective, partly cut away and partly in cross section, of a modified embodiment of the improved high reactance transformer of this invention; and

Figure 3 is a view in perspective of the elongated core member of the transformer of Figure 2.

Referring now to Figure 1 of the drawing, there is shown a high reactance transformer, generally indicated as 1, having an elongated core member 2 formed of a stack of relatively thin laminations of magnetic material 3. The laminations 3 may be cut from a narrow strip of relatively thin magnetic material, thus substantially eliminating all waste. Spaced apart coils 4 and 5 are arranged on the elongated core member 2 and are spaced from the end portions 6 and 7 thereof. Coil 4 may, for example, be the primary winding for the transformer and coil 5 would thus be the secondary winding therefor.

In order to complete the magnetic circuit for elongated core member 2 the arrangement now to be described is provided. A pair of yoke core members 8 and 9, each formed of a wound strip of relatively thin magnetic material, is provided; each of the core members 8 and 9 cmbraces coil 4 on opposite sides 10 and 11 respectively of elongated core member 2, as shown. Another pair of yoke core members 12 and 13 are similarly arranged embracing coil 5 on opposite sides ill and 11 of elongated core 2. Portions 14 and 15 of core members 8 and 12 respectively are arranged so as to be in abutting relationship and have their laminated edges completing magnetic circuits with side Ill of core member 2. Portions 17 and S of core members 9 and 13 respectively are similarly arranged in abutting relationship with each other and with side 11 of elongated core member 2. Portions 14 and 15 of core members 8 and 12 respectively and portions 17 and 18 of core members 9 and 13 respectively thus form magnetic shunts for the high reactance transformer 1. The necessary shunt air gaps are provided by means of insulation 16 (seen only in connection with portions 14 and .15) which may, for instance, be formed from any standard insulating tape. Portions 19 and 20 of core members 8 and 9 respectively have their laminated edges respectively completing magnetic circuits with sides 10 and 11 respectively of end portion 6 of elongated core member 2 by direct engagem nt therewith. In exactly similar fashion (although not shown), portions 21 and 22 of core members 12 and 13 respectively have their laminated edges respectively completing magnetic circuits with sides 10 and 11 of end portion 7 of elongated core member 2. Wound yoke core members 8, 9, 12 and 13 provide paths for leakage flux and also form magnetic shunts with the elongated core member 2.

V A third pair of wound yoke coremembers 23 and 24 are provided, formed in planes substantially perpendicular to the planes in which yoke core members 8, 9, 12 and 13are wound. Each of the yoke wound 'core members 23 and 24 embraces both coils 4 and and all four of the yoke core members 8, 9, 12 and 13. Portions 25 and 26 of wound yoke core members 23 and 24 have their laminated edges respectively completing magnetic circuits with the laminated sides 27 and 28 of elongated member 2 at end portions 6. In exactly similar fashion (but not shown), portions 29 and 30 of wound yoke core members 23 and 24 have their laminated edges respectively completing magnetic circuits with laminated sides 27 and 28 of elongated core member 2 at end portion 7 thereof.

Insulating strips 31 may be provided along the laminated sides 27 and 28 of elongated core member 2 so that a series air gap may be formed between portions 25 and 26 of core members 23 and 24 respectively and end portions 6 of core member 2. The wound yoke core members 23 and 24 provide the flux paths for the mutual fiux which links both coils 4 and 5.

It will now be seen that the improved high reactance transformer construction of Figure 1 is accomplished with minimum waste of core material and that wound cores provide paths for both the leakage flux and the mutual flux. It will also be seen that the flux paths and the requisite air gaps are provided without the necessity for cutting any of the wound cores. In addition, the arrangement of core members 23 and 24 at right angles to core members 8, 9, 12 and 13 permits a substantial reduction in the amount of magnetic material required for the core members 23 and 24. This results from the fact that these core members are required to extend around the core members 8, 9, 12 and 13 only at the end of the transformer and not along the entire side of the transformer. As a result, substantially less magnetic material is required to provide a flux path with a cross sectional area equal to that provided before at the expense of more magnetic material.

Referring now to Figures 2 and 3 of the drawing in which like elements are indicated by like reference numerals, there is shown a high reactance transformer, generally indicated at 32, which is generally similar in construction to transformer 1 shown in Figure 1, but which is providedwith a modified elongated core mem her 33 which is made up of three separate parts 34, 35, and 36. Each part is made up of a plurality of thin laminations 3 of magnetic material. It will again be seen that the laminations 3 for all the parts 34, 35, and 36 may be cut from narrow strips of relatively thin magnetic material, thus eliminating waste, as for the embodiment of Figure 1. Center part 35 of elongated core member 33 extends beyond outer parts 34 and 36 at the end portions 37 and 38 of core member 33. Part 35 will, then, have a pair of laminated sides 39 and 4t) protruding at each end. Parts 34 and 36 are arranged so that the laminations are stacked perpendicular to the direction of stacking for part 35. By this stacking arrangement, sides 41 and 42 of part 36 and sides 43 and 44 of part 34 are also laminated in the same manner as sides 39 and of part 35. The fact that center part, 35 extends beyond either of parts 34 and 36 at each end permits the laminated side of wound yoke core members 23 and 24 to complete a magnetic circuit with the laminated sides 39 and 40 respectively of center part 35. As before, strips 31 of insulation may be provided so as to, afford a series air gap. The'provision. of parts 34 and 36 with their laminated sides 41 and 42, and 43 and 44 respectively permits the leakage flux path to be completed exclusively across the laminated side portions of the members. This arises from the fact that end portions 19 and 20 of core members 8 and 9 respectively will have their laminated sides in abutment with the laminated sides 42 and 41 respectively of part 36 and laminated sides 44 and 43 respectively of part 34 at end 37 of elongated core member 33. A similar engagement is provided for portions 14 and 15 of core members 8 and 12 respectively intermediate the coils 4 and 5 and for portions 17 and 18 of core members 9 and 13 respectively intermediate the coils 4 and 5. In the same fashion, portions 21 and 22 of core members 12 and 13 respectively abut sides 42 and 44 and sides 41 and 43 respectively of portions 36 and 34.

The embodiment of Figures 2 and 3 incorporates the advantageous feature that in no case does a single outer or inner lamination lie fiat against another core member with the intent of having magnetic flux pass therethrough; instead, flux will always be transferred between members through their laminated sides. It is known that the transference of flux through a single lamination to other laminations causes edd'y'fiuxes which detract from the proper performance of the high reactance transformer; the embodiment of Figures 2 and 3 completely avoids such eddy fluxes. At the same time, the embodiment of Figures 2 and 3 retains the advantageous feature of this invention, in that the amount of magnetic material needed for core members 23 and 24 is cut substantially below the amount previously necessary without any decrease in the cross-sectional area available for the flow of flux.

While this invention has been explained by describing particular embodiments thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention as defined in the appended clairns.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high reactance transformer comprising an elongated core member formed of magnetic material, at least two spaced apart coils positioned on said elongated core member and respectively spaced from the end portions thereof, a first yoke core member formed of a wound strip of magnetic material embracing one of said coils and extending adjacent a side of one end portion of said elongated core member, a second yoke core member formed of a wound strip of magnetic material embracing another of said coils and extendingadj acent a side of the other end portion of said elongated core member, at least one of said first and second yok e core members extending adjacent said elongated core meinb er intermediate said coils to form a magnetic shunt for said transformer, and a third yoke core memberformed of a wound strip of magnetic. material embracing-both said coils and said first and second yoke core members and extending adjacent both said end portions of said elongated core members, the windings of said third yoke core member being in planes substantially perpendicular to the planes of the windings of. said first and second yoke core members.

2. A high reactance transformer comprising an elongated laminated core member formed of magnetic material, at least two spaced apart coils positioned on said elongated core member and respectively spaced from the end portions thereof, a first pair of yoke core members each formed of a wound strip of magnetic material and each arranged to embrace one of said coils adjacent opposite sides of one end portion of said elongated core member, a second pair of yoke core members each formed of a .woundstrip of magnetic material and each arranged to embrace another of said coils adjacent opposite sides of the other-end portion of said'elongated core member, said first pair of core members and said second pair of core members respectively abutting one another intermediate said coiis thereby to form.magnetic shunts for said transformer, and a third pair of yoke core members each formed of a wound stripjof magneticmaterial and arranged to embrace both of said coils and said first and second pairs of yoke core members, each of said third pair of core members extending adjacent both end pertions of said elongated core member end portions on opposite sides thereof, said third pair of yoke core members having its windings in parallel planes substantially perpendicular to the planes of the windings of said first and second pairs of yoke core members.

3. A high reactance transformer comprising an elongated core member formed of magnetic material, at least two spaced apart coils positioned on said elongated core member and respectively spaced from the end portions thereof, a first yoke core member formed of a wound strip of magnetic material embracing one of said coils and abutting one side of one end portion of said elongated core member, a second yoke core member formed of a wound strip of magnetic material embracing anotner of said coils and abutting said one side of the other end portion of said elongated core member, at least one of said yoke core members extending adjacent said elongated core member intermediate said coils to form a magnetic shunt for said transformer, and a third yoke core member formed of magnetic matrial embracing both sald coils and said first and second yoke core members 1nd arranged to abut said end portions of said elongated core member along a side thereof perpendicular to said one side, said third yoke core member having its windings in planes substantially perpendicular to the planes of the windings of said first and second yoke core members.

4. A high reactance transformer comprising an elongated laminated core member formed of magnetic material, at least two spaced apart coils positioned on said elongated core member and respectively spaced from the end portions thereof, a first pair of yoke core members each formed of a wound strip of magnetic material and each arranged to embrace one of said coils abutting opposite sides of one end portion of said elongated core member, a second pair of yoke core members each formed of a wound strip of magnetic material and each arranged to embrace another of said coils abutting opposite sides of the other end portion of said elongated core member, said first pair of core members and said second pair of core members respectively having sides thereof in abutting relationship intermediate said coils thereby to form magnetic shunts for said transformer, and a third pair of yoke core members each formed of a wound strip of magnetic material and arranged to embrace both of said coils and said first and second pairs of yoke core members, each of said third pair of core members abutting said end portions of said elongated core member on opposite sides thereof, said third pair of yoke core members having their windings in planes substantially perpendicular to the planes of the windings of said first and second pairs of yoke core members.

5. A high reactance transformer comprising an elongated core member having at least two superimposed parts each formed of a stacked plurality of thin laminations of magnetic material, one of said parts being arranged with its laminations substantially perpendicular to the laminations of the other part, at least two spaced apart coils positioned on said elongated core member and respectively spaced from the end portions thereof, a first yoke core member formed of a wound strip of magnetic material embracing one of said coils and having a laminated side thereof abutting a laminated side of said one part at one end portion of said elongated core member, a second yoke core member formed of a wound strip of magnetic material embracing another of said coils and having a laminated side abutting the laminated side of said one part at the other end portion of said elongated core member, at least one of said yoke core members having a laminated side arranged adjacent a laminated side of said one part intermediate said coils thereby to form a magnetic shunt for said transformer, and a third yoke core member formed from a wound strip of magnetic material embracing both said coils and said first and second yoke core members and having a laminated side arranged to abut a laminated side of said other part at the end portions of said elongated core member, said third yoke core member having its windings in planes substantially perpendicular to the planes of the windings of said first and second yoke core members.

6. A high reactance transformer comprising an elongated core member having a center part formed of a stacked plurality of thin laminations of magnetic material, said elongated core member further having two outer parts respectively abutting opposite laminated sides of said center part, each of said outer parts being formed of a plurality of thin laminations of magnetic material stacked in a direction substantially perpendicular to the direction of stacking of said center part, said center part having end portions extending beyond the end portions respectively of said outer parts thereby to expose the laminated sides of said center part, at least two spaced apart coils positioned on said elongated core member and respectively spaced from the end portions thereof, a first pair of yoke core members each formed of a wound strip of magnetic material and arranged to embrace one of said coils, each of said pair of members abutting opposite laminated sides at the end portions of said outer parts at one end portion of said elongated member, a second pair of yoke core members each formed of a wound strip of magnetic material and arranged to embrace another of said coils, each of said second pair of members abutting opposite laminated sides of the end portions of said outer parts at the other end portion of said elongated core member, the adjacent laminated sides of each of said first and second pairs of yoke core members being arranged in abutting relationship respectively adjacent opposite laminated sides of said outer parts intermediate said coils thereby to form a magnetic shunt for said transformer, and a third pair of yoke core members each formed from a wound strip of magnetic material and arranged to embrace both of said coils and said first and second pairs of yoke core members, each of said third pair of members abutting opposite laminated sides at each end portion of said center part, said third pair of yoke core members having its windings in parallel planes substantially perpendicular to the planes of the windings of said first and second pairs of yoke core members.

References Cited in the file of this patent UNITED STATES PATENTS 2,771,587 Henderson Nov. 20, 1956 FOREIGN PATENTS 554,384 Great Britain July 1, 1943 

